Disk head assembly with multiple read and / or write transducers for improved performance

ABSTRACT

A recording disk apparatus is provided. The recording disk apparatus includes a recording disk having at least one recording surface with a plurality of spaced recording tracks. The recording disk also includes a positioning arm with a head assembly. The head assembly has a plurality of read transducers. Each consecutive transducer is positioned relative to one another at a distance substantially smaller than a spacing between two consecutive tracks.

BACKGROUND OF THE INVENTION

1. (1) Field of the Invention

2. The present invention pertains to the field of disk drives. Moreparticularly, the present invention pertains to apparatus and methodthat utilize a head assembly to read and/or write information from/tothe disk drive.

3. (2) Background Information

4. One of the key components for certain electrical devices is a placeto store data thereon and read data therefrom. For example, compact diskplayers read data, such as music, from a plastic disk. Another exampleis a VCR which reads data (video information) from a tape. Computersystems are endowed with devices that may store thereon and from whichit may be read therefrom large amounts of data. Computer systems employa variety of storage devices to store data. One of these devices is adisk drive, which may also be a direct access storage device. FIG. 1shows a disk 100 onto which data is stored in concentric circular tracks102. A first track 116 is the closest to a spindle 106.

5. A disk drive 100, or direct access storage device, includes severaldisks 104 which look similar to records used on a record player, orcompact disks which are used in a C.D. player. The disks are stacked onspindle 106, much like several records waiting to be played. In a diskdrive, however, the disks are mounted into the spindle and spaced apartso that the separate disks do not touch each other.

6. Information is recorded on a surface 110 of each disk. The surface110 of each disk 104 is uniform in appearance. However, in actuality,each of the surfaces is divided into portions where data is stored.There are a number of tracks 102 disposed in concentric circles likerings on a tree. Each track in a disk drive is further subdivided into anumber of sectors of which sectors 117, 118, 119, and 120 are shown inthe Figure. Each sector is essentially just one section of thecircumferential track.

7. The recorded information is divided into sectors. Servo informationis recorded in radially continuous narrow wedges (not shown) betweensectors. The information in the servo sections includes: track number;sector number; and tracking information.

8. Storage of data on a magnetic disk entails magnetizing portions ofthe disk in a pattern which represents the data. To magnetize the disk,a small ceramic block which contains a magnetic transducer known as a“write element” is passed over the surface of the disk. Morespecifically, the write element is flown at a height of approximatelysix-millionth of an inch from the surface of the disk over the track.The write element is energized to various states, causing the trackbelow to be magnetized to represent the data to be stored.

9. To retrieve data stored on a magnetic disk, a read element is flownover the disk. The magnetized portions of the disk provide a signal tothe read element. By looking at output from the read element, data canbe reconstructed and then be used by the computer system.

10. Like a record, both sides of a disk are generally used to store dataor other information necessary for the operation of the disk drive.Since disks are held in a stack and are spaced apart from one another,for both the top and the bottom surface of each disk in the stack ofdisks there is a corresponding read element and write element. Thiswould be comparable to a stereo that would play both sides of a recordat once. Each side has a stylus which may play the particular side ofthe record.

11. There are two types of disk drives: rotary and linear. Rotary diskdrives have a tone arm that rotates much like a record player. The tonearm of a rotary disk drive, termed actuator arm, holds all thetransducers or read/write elements—one head for each surface of eachdisk supported in a structure that looks like a comb. Like a tone arm,the actuator arms rotate so that the read element and write elementattached to the actuator arm can be moved to locations over varioustracks on the disk. In this way, the write element can be used tomagnetize the surface of the disk at one of several tracks locations ina pattern representing the data. The read element is used to detect themagnetized pattern on one of the tracks of a disk. For example, theneeded data may be stored on two different tracks on one particulardisks, so to read the magnetic representations of the data, the actuatorarm is rotated from one track to another track.

12. Before writing or reading, the magnetic head must be positioned inclose proximity of or above the correct track. This is accomplished bymounting the head on an arm that moves radially, or in an ark to thesection of the disk allocated to the write/read operation. In rigid diskdrives, many head assemblies and support arms are mounted on one commoncarriage that is moved as one unit. This is shown in FIG. 2 where afour-platter disk drive 202 is shown with a head carriage 204 moved backand forth by linear voice-coil motor (VCM) 216 that may be identical tothe “motor” in a loudspeaker. In linear disk drives, typically, for eachdisk (platter) 210 there is a double positioning arm 212 that positionsthe head onto a specific track by virtue of linear movement of the headcarriage 204, to which the positioning arm 212 is mounted. FIG. 3 showsa top view of a disk 302 coupled to a linear VCM 304. A linear actuatoris disposed inside carriage 306. The actuator is coupled to thepositioning arm 308 that has a head mounted at a free end thereof. Theactuator causes the head to shift to new track positions.

13. Rigid disk drives demand fast and precise positioning of the head.At low track densities, it is relatively easy to position the head; athigher densities, it is necessary to use a track-following technique, byusing a closed-loop servo. Overall performance of a disk drive ismeasured by its seek time, which is the average time it takes for a headto move from one track to another (including time to settle over thetrack), plus the latency, which is the time for one revolution (some maysay that the average latency represents the time for one-halfrevolution).

14. The access time (to a track) is in the approximate range of 10-30milliseconds (ms). To position a head accurately, full-forward power ofthe actuator is applied for half the time required. Then reverse poweris applied until the actuator comes to zero velocity. When the processis done, if the control system functions properly, it may position thehead precisely on target. This is what servo engineers call a“bang-bang” control.

15. The servo system keeps track of where the head is. This is typicallydone with a difference counter that contains the number of tracks to thetarget. The difference counter is updated as tracks are crossed. Whenthe head has been positioned over the right track, the next task for thedisk controller's servo system is to keep the head on track irrespectiveof mechanical vibrations, aerodynamics disturbances, or changes due tovariations in the temperature.

16. At high-track densities, a direct position feedback from the headitself is necessary to correct for any mistracking. Trackmisregistration (TMR) may be caused by several items: spindle run-out;resonances and disk flutter; thermal track shift; head settling;actuator interaction; and improper servo writing. A disk drive's TMR istherefore a summation of all the head position errors summed up over aperiod of time.

17. Stringent requirements are posed on the head and the mechanism thatcontrols the head such as track-to-track access time, accuratepositioning of the head by the servo-mechanism, and reading by the headfrom the storage device when the head has stopped moving completely. Itis desirable to provide a disk-head assembly with improved performance,including decreased track-to-track access times, where reading of datamay be performed even when the head has not necessarily been stoppedfrom moving completely. It is also desirable to compensate for effectssuch as spindle run-out, resonance and thermal effects without having tomove the heads as much or as rapidly as current systems require.

SUMMARY OF THE INVENTION

18. The present invention provides a recording disk apparatus. Therecording disk apparatus includes a recording disk having at least onerecording surface with a plurality of spaced recording tracks. Therecording disk also includes a positioning arm with a head assembly. Thehead assembly has a plurality of read transducers. Each two consecutiveread transducers are positioned relative to one another at a distancesubstantially smaller than a spacing between two consecutive recordingtracks.

BRIEF DESCRIPTION OF THE DRAWINGS

19. The features, aspects, and advantages of the present invention willbecome more fully apparent from the following Detailed Description,appended claims, and accompanying drawings in which:

20.FIG. 1 shows a disk with a number of platters, tracks, and sectors;

21.FIG. 2 shows a four-platter disk drive with a head carriage driven bya linear voice-coil motor;

22.FIG. 3 shows a top view of a disk coupled to a linear voice-coilmotor that drives a positioning arm;

23.FIG. 4 illustrates in a simplified form a recording disk apparatuswith a head assembly with multiple read transducers according to oneembodiment of the present invention;

24.FIG. 5 illustrates in diagramatic form three tracks and fourtransducers of an array of transducers according to one embodiment ofthe present invention;

25.FIG. 6 illustrates a block diagram of an electronic circuit inconnection with a disk recording apparatus with a head assembly withmultiple read transducers according to one embodiment of the presentinvention; and

26.FIG. 7 illustrates a flow chart diagram in connection with a methodfor reading data from a recording disk according to one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

27. In the following description, numerous specific details are setforth to provide a thorough understanding of the present invention.However, one having ordinary skill in the art should recognize that theinvention may be practiced without these specific details. In someinstances, well-known circuits, structures, and techniques have not beenshown in detail to avoid obscuring the present invention.

28.FIG. 4 illustrates a recording disk apparatus with a head assemblywith multiple read transducers according to one embodiment of thepresent invention. The recording disk apparatus 400 includes at leastone recording disk 402 (hereinafter referred to as “disk 402”) which, inone embodiment described herein is a hard disk, but the presentinvention is not limited to a hard disk. The present invention may applyto other storage devices, magnetic or non-magnetic. The disk 402 isshown from the top, with a top-most platter 408, being understood thatthe disk drive includes a plurality of disk platters distanced from oneanother and positioned on spindle 406. Platter 408 includes a pluralityof radial tracks 410. The spacing between tracks 410 may be around{fraction (1/10,000)}inch, i.e. 10,000 tracks per inch.

29. The recording disk apparatus 400 includes a positioning arm 412 thathas at a free end thereof a head assembly 414 (shown in dotted lines).The head assembly 414 includes an array of transducers 416. In oneembodiment according to the present invention, transducers 416 are“read” transducers. In other embodiments of the present invention,transducers 416 may be “write” transducers. In one embodiment of thepresent invention, transducers 416 are fixedly positioned, relative toone another. Two consecutive transducers are positioned at a distance430 there between substantially smaller than a spacing 432 between twoconsecutive tracks 410. The distance between two transducers is definedherein as the horizontal component of a vector that joins the centers417 of two consecutive transducers.

30. The recording disk apparatus has a positioning arm 412 for eachrecording platter 408. For each surface 404 of each platter, there is anarray 414 corresponding thereto. The arrays 414 are moved by thecorresponding positioning arms 412 at the same time. The positioning arm412 is mounted on a head carriage 422 which is coupled to a linearvoice-coil motor (VCM)424 that produces the linear motion of the headcarriage. The array 414 is designed such that at least one transducer416 may properly read a certain track at a given point in time.Therefore, there is at least one transducer producing a good signalderived from the target track. While the head assembly 414 (shown in theFigure) includes 4 transducers, the head assembly may be implemented tohave more or less than 4 transducers.

31. As rotation occurs, if the array 414 is wide and dense enough (i.e.,many transducers per unit of space), one of the transducers may read oneof the tracks that otherwise may not have been read due to the amount ofrun-out (eccentricity). Accordingly, in this case, there may be no needfor a real-time feedback loop to constantly operate to track theeccentricity in the motion.

32. Typically, the separation between two consecutive transducersdepends on how close a transducer needs to be to a track to read it. Theseparation between tracks is one factor in determining how close atransducer has to be to a particular track that is to be read. Since thestrength of the signal that each track generates in the transducerdepends on the distance from the track to the transducer, the transducermust be closer to the target track than to any other track. The degreeto which transducers have to be closer depends on the signal-to-noiseratio. The “signal” represents the signal from the targeted track thatis to be read out. The “noise” is a signal from a track other than thetarget track that is not desired to be read out at a specific time. Theminimum required signal-to-noise ratio for the signal may require thatthe transducers be as close as possible to the track. In one embodimentaccording to the present invention, the transducers are separated by aspace that represents approximately 70% of the track-to-track distance.

33.FIG. 5 illustrates in diagramatic form three tracks and fourtransducers of an array of transducers 506 of a head assembly accordingto one embodiment of the present invention. In this figure D_(TT) is thetrack-to-track spacing (i.e., the distance between the centers of twoconsecutive tracks), while D_(HH) is the transducer-to-transducerdistance (i.e., the distance between the centers of two consecutivetransducers). Assume that P is the head assembly's position (determinedby the positioning arm). The radial position of a transducer “N” isP+N×D_(HH) where “N” is the number of the transducer (i.e., “N” is theNth transducer) when transducers are counted from the head assembly'sposition P towards the periphery of the disk. The radial position oftrack “M” is M×D_(TT), where M is the number of the track (i.e., “M” isthe Mth track) when tracks are counted from the center of the disk.

34. Assume that 508 (“N”) is positioned to the left of track 510 (“M”),X₁=(M×D_(TT)−P+N×D_(HH)) mod D_(HH)=(M×D_(TT)−P) mod D_(HH), where X₁ isthe distance between the center of the track (510) and the center of thetransducer 508. Using the same mathematical formalism, X₂=(P+(N+1)×D_(HH)−M×D_(TT))mod D_(HH)=(P−M×D_(TT)) mod D_(HH)=D_(HH)−(M×D_(TT)−P)mod D_(HH). Note that (M×D_(TT)−P) mod D_(HH) can assumevalues from 0 to D_(HH). If (M×D_(TT)−P)mod D_(HH)<D_(HH)/2, X1 is lessthan X2. If (M×D_(TT)−P) mod D_(HH)>D_(HH)/2, X₂ is less than X₁.Therefore, the minimum value between X1 and X2, min(X1,X2)<=D_(HH)/2,which is to say that in the embodiment of the present inventiondescribed herein, at least one transducer is less than D_(HH)/2 awayfrom the target track if the target track is located within the array oftransducers. Even if the position of the positioning arm (not shown)varies, as long as the target track is still under the array oftransducers, some transducer of the array is positioned within half thetransducer-to-transducer spacing from the target track. This alsoapplies if the position of the tracks varies (due to run-out) as may befound by measuring the run-out relative to the position of the headassembly.

35. To obtain a usable signal from the target track, transducers arepositioned away from the target track at distances equal to or lesserthan a track-to-transducer spacing (D) that produces a usable signal.Since D_(HH)/2≦D and D≦D_(TT)/2, it follows that D_(HH)≦D_(TT). Thismeans that the distance D_(HH) between two consecutive transducers mustbe equal to or smaller than the distance D_(TT) between two consecutivetracks.

36. If consecutive transducers are spaced relative to each other closerthan twice the minimum required track-to-transducer distance (i.e.,D_(HH)≦2D), then as long as a track stays underneath the transducerarray, one of the transducers, of the array of the recording apparatusaccording to the embodiment of the present invention, is closer to atrack than the minimum required track-to-transducer distance D, andtherefore is able to produce a proper (accurate) signal for this track.This remains true even if the transducer array moves slightly (due tothermal or resonance effects, or because the heads have not comeentirely to a stop yet) or the track wobbles as the disk rotates.

37. When two consecutive transducers are positioned within twoconsecutive tracks at equal distances from the tracks adjacent to eachtransducer, both transducers may produce good signals derived from thetracks adjacent thereto. The design ensures that the track-to-transducerdistance is lower than the minimum required track-to-transducerdistance.

38. When two consecutive transducers are positioned on each side of atrack, one of the transducers will detect a good signal for thatrespective track as the distance between the two transducers is lowerthan twice the minimum required track-to-transducer distance—one of thetransducer will be closer to a targeted track than the minimum requireddistance D. The requirement that two transducers be positioned at adistance lower than twice the minimum required distance (2D) ensuresthat at least one of the two transducers, on each side of a track,properly reads that track's signal.

39. Electronic circuits coupled to the transducers may determine whichtransducer is closest to the target track in real time using techniquescommonly utilized nowadays in hard disk drives. Also, the electroniccircuits may switch control from one transducer to another in the middleof the read operation, and join the outputs of the transducers in such amanner as to prevent the switch from one transducer to another fromcorrupting output data.

40. A system may be provided where a head with multiple transducers maybe utilized for each surface of a platter of a disk drive in the mannerdescribed above. The system may utilize a single write head that may beemployed in a manner known to people of ordinary skills in the art. Thewrite head may be positioned over the correct track by monitoring oneread transducer in the array of transducers that was positioned at thesame distance away from the center of the disk's rotation as the writehead. It should be appreciated by persons having ordinary skills in theart that a system could possibly use multiple write heads in anarrangement similar to that described in connection with readtransducers.

41. By reading out with a read transducer one may determine when a head(transducer) is on the right track. Therefore, the information aboutwhich write head is to be utilized may be based on the informationcoming from the read array. Thus, one needs to get information out fromthe read heads to know whether the write head or write heads arepositioned correctly. Then one may pick the write head that is mostappropriate, i.e. closest to the track desired to be written on thattrack. While a write operation is performed, the initially selectedwrite head must continue to be the write head used: write heads may notbe switched in the middle of a write operation the way read transducersmay be switched during a read operation.

42. Typically, read heads are not spliced—each has its own connectionback to the electronics shown in FIG. 6. The same may apply if there aremultiple write heads, or they might share a common “ground” wire.

43.FIG. 6 illustrates a block diagram of an electronic circuitconfigured to read data from the tracks of a disk by two transducers ofan array of transducers. Transducers 602 and 604 are two transducers ofa head assembly of an array 414 (as shown in FIG. 4) or 506 (as shown inFIG. 5) that are implemented in one embodiment according to the presentinvention as two magneto-resistive elements. Due to the certain amountof run-out, one of the transducers of the array, at a certain point intime, may be more likely to read more accurately certain data from thetrack and mostly to produce a signal that has a strength that moreaccurately reflects that data. Accordingly, at times, it may be requiredto switch from one transducer to the other so that one reads from thetransducer that is more closely positioned to the desired portion of thetrack to be read out.

44. In the circuit 600, the two transducers 604 and 602 read in ananalog fashion data from a track and convey it into an analog signal.The analog signal is driven to the amplifiers 606 and 608, correspondingto the transducers 602 and 604 respectively, where the signal isamplified.

45. From the amplifiers 606 and 608, data is driven to a correspondingdiscriminator 616 or 614, which converts the analog signal into adigital signal giving rise to bit streams. Measuring circuits 610 and612 are coupled in parallel with the discriminators to analyze theanalog signals coming off the amplifiers and determine whether theanalog signals are clean signals coming off of a single track or if thesignals are “dirty” because a particular transducer was positionedbetween two tracks. Implementation of the quality measuring circuit maybe performed in different ways. One may look at the absence or lack of aparticular frequency spectrum at the output of the amplifier, or one mayjust look at the signal strength in general and determine whether thesignal is a strong enough signal or not. Implementation of the qualitymeasuring circuit is within the ambit of persons skilled in the art.Detection of whether the information collected by a transducer iscorrect may be also performed by using error-detecting codes built intothe data written down onto the disk drive.

46. Blocks 618 and 620 represent circuits designed to perform qualityanalysis of the outputs of the discriminator, based on the bit streams,using common techniques known to persons having ordinary skills in theart. Blocks 622 and 626 represent circuits that combine the analogsignal derived and digital signal derived quality metrics. Analogsignals derived from signals quality-metrics may not be needed if theconverted bit streams may supply quality data (for example, by thenumber of invalid codes in the bitstream). Once a lot of errors arefound, one may conclude that the transducer is not aligned correctly.

47. Circuit 600 may also extract information about what track and sectora transducer is on. That information may be embedded in the magneticfield of the track. For each transducer, one has 3 signals output bycircuit 600. First, one has a bitstream coming out of devices 616 and614, going to buffers 630 and 632 respectively. One may have a signalthat denotes quality coming out of circuits 622 and 626, and a signalthat represents the location of a transducer. The location is detectedby position-detection circuits 624 and 628. Based on the quality and thelocation detected, one may select which of the transducers had theinformation one desires.

48. When switching bitstream buffers in the middle of a read operation,it may occur that the bitstream from one transducer is slightly out ofsync with the bitstream from the other transducer. The bitstream bufferscan store sufficient data to permit the two streams to be mergedtogether correctly as one switches from one transducer to the othertransducer, so that no bits are dropped and no bits are duplicated. Thismay be accomplished by pattern matching between the two bit streams orby a built-in knowledge of the physical location of each transducer (andtherefore the temporal skew in the bit streams from each transducer), ora combination of both. The bitstream buffers 630 and 632 then may beconnected to a selecting device such as a multiplexer that may becontrolled by the location signals coming out of the position detectioncircuits 624 and 628.

49. If two tracks on the same surface are both within the area coveredby the array of transducers, both may be readout simultaneously. Also,since fine tracking of a track being read are resolved within each arraywithout moving or in any way affecting all the other head arrays, it ispossible to read a track out from every surface of the disk drivesimultaneously.

50. The present invention also provides, in one embodiment thereof, amethod for reading data from a recording disk. FIG. 7 illustrates a flowchart diagram of an embodiment of the method of reading data from arecording disk according to one embodiment of the present invention. Themethod starts at block 702 from where it passes to block 704. At block704 an arm, with a head assembly has a plurality of read transducers, ispositioned above a plate of a recording apparatus. The method flows toblock 706 where it is determined which transducers is closest to atargeted track. At block 708 control is switched to the closest readtransducer. At block 710, it is detected whether information collectedby at least one transducer is correct. At block 712, a bitstreamrepresenting information read from the targeted track is provided.

51. In the foregoing specification, the invention has been describedwith reference to specific embodiments thereof. It will however beevident that various modifications and changes can be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense. Therefore, the scope of the invention should be limited only bythe appended claims.

What is claimed is:
 1. A recording disk apparatus comprising: arecording disk having at least one recording surface with a plurality ofspaced recording tracks; and a positioning arm with a head assembly,said head assembly having a plurality of read transducers, each twoconsecutive read transducers positioned relative to one another at adistance substantially smaller than a spacing between two consecutiverecording tracks.
 2. The recording disk apparatus of claim 1 wherein twoconsecutive transducers are spaced closer than twice a minimum requiredtrack-to-transducer distance.
 3. The recording disk apparatus of claim 1wherein one transducer positioned away from an adjacent track, at adistance that is equal to or less than half the distance betweenconsecutive transducers.
 4. The recording disk apparatus of claim 1further including an actuator coupled to the positioning arm.
 5. Therecording mechanism of claim 1 further including a signal processingdevice coupled to said plurality of transducers.
 6. The recordingmechanism of claim 1 wherein said read transducers are magnetictransducers and said recording disk is a magnetic recording disk.
 7. Therecording disk apparatus of claim 1 further including a motor connectedto said head assembly.
 8. The recording disk apparatus of claim 1 , saidpositioning arm mounted on a head carriage coupled to a linearvoice-coil motor (VCM)
 9. The recording disk apparatus of claim 1further including a write head.
 10. The recording disk apparatus ofclaim 1 further including for each read transducer a bitstream buffer.11. The recording disk apparatus of claim 1 further including electroniccircuits coupled to the transducers to determine which transducer isclosest to a targeted track.
 12. The recording disk apparatus of claim 1further including a position detecting circuit.
 13. The recording diskapparatus of claim 1 further including a circuit that detects signalquality.
 14. A computer system comprising: a processor; a memory coupledto the processor; and a disk drive coupled to said processor, said diskdrive including a recording disk having at least one recording surfacewith a plurality of spaced recording tracks; and a positioning arm witha head assembly, said head assembly having a plurality of readtransducers, each two consecutive read transducers positioned relativeto one another at a distance substantially smaller than a spacingbetween two consecutive tracks.
 15. The computer system of claim 13wherein two consecutive transducers are spaced closer than twice aminimum required track-to-transducer distance.
 16. The computer systemof claim 13 where one transducer positioned away from an adjacent trackat a distance that is equal to or lesser than half the distance betweenconsecutive transducers.
 17. The computer system of claim 14 furtherincluding an actuator coupled to the positioning arm.
 18. The computersystem of claim 14 further including a signal processing device coupledto said plurality of transducers.
 19. The computer system of claim 14wherein said read transducers are magnetic transducers and saidrecording disk is a magnetic recording disk.
 20. The computer system ofclaim 14 further including a motor connected to said head assembly. 21.The computer system of claim 14 , said positioning arm mounted on a headcarriage coupled to a linear voice-coil motor (VCM).
 22. The computersystem of claim 14 further including a write head.
 23. A method forreading data from a recording disk, the method comprising the steps of:a. positioning an arm, with a head assembly that has a plurality of readtransducers, above a plate of the recording disk; b. determining whichread transducer is closest to a targeted-track; c. switching to theclosest read transducer; d. detecting whether information collected byone read transducer is correct; and e. providing a bitstreamrepresenting information read from said targeted track.